About half of the neutrinos detected from natural, underground sources come from the Earth’s mantle, rather than the crust, according to an analysis of new neutrino detection data.

“For those of us in the field, this is very impressive progress,” says Jason Detwiler of the University of Washington in Seattle, a member of the KamLAND group. “Their spectrum is very clean and beautifully and incontrovertibly demonstrates the presence of the geoneutrino signal.” Detwiler says that the number of mantle neutrinos seen by Borexino may have geophysical significance. ”The data are consistent with there being enough radiogenic heat to drive mantle convection,” he says, referring to the slow turnover of mantle material over geologic time.